1. Field of the Invention
The present invention relates to a wide band wireless communication system. More particularly, this invention relates to a local multipoint distribution service(LMDS) system which can provide subscribers who are networked through a wireless network with a variety of wireless multimedia service, such as a wireless local loop(WLL), a local area network(LAN), a community antenna television system(CATV), etc.
2. Description of the Related Arts
According to a recent day high computerization, mobile network companies have been developing communication systems capable of servicing any format of data in any place at any time. In this situation, a cable multimedia communication system was provided, which used as data various information, such as characters, numerals, image and audio data, etc. However, in the cable multimedia communication system, it takes very long times to construct a whole network, and the network must be replaced every 7 years to keep high quality images. Moreover, the cable is vulnerable to natural calamity, such as a rainfall, a snowfall, etc.
Therefore, to improve the above problems, a wide band wireless multimedia communication system has been developed. However, the wireless multimedia communication system has not yet become common, and companies do not need to open their knowhow about it.
One of the wide band wireless communication systems, is a local multipoint distribution service(LMDS). LMDS is a wide band wireless commercial network service which provides a super-high speed wide band multimedia service using a subscriber""s loop frequency band of a millimeter wave band, whose upstream frequency is from 24.25 to 24.75 GHz and downstream frequency is from 25.5 to 27.5 GHz. Service items are a voice telephone, a data communication, a conversational image service, an audio-data-image-combined multimedia service, a line leasing service, etc. Subscribers can be public citizens, private network subscribers, public network transfer relayers, etc. Service area is about 2-5 km. Now DAVIC(Digital Audio-Visual Council) is suggesting a standard specification for LMDS.
FIG. 1 is a brief structure of a conventional wide band wireless multimedia communication system. In construction, a general wide band wireless multimedia communication system is organized by a central office 20 for multiplexing packet data and supervising a whole network and every subscribers; a plurality of head ends 2 for demultiplexing traffic signals from the central office 20 and modulating the demultiplexed signals into optical signals, or for demodulating and multiplexing optical signals received and transferring the multiplexed signals to the central office 20; a plurality of base stations 30 for converting optical signals from the head ends 2 into electrical signals and amplifying it to transmit to the receiving end subscriber, or for converting the radio frequency(RF) signals received from the sending end subscriber into intermediate frequency(IF) signals and converting them into optical signals to transmit to the head ends 2; and a customer premises equipment(CPE) 40 for treating the signals received from the base stations 30 and provides the treated signals to final peripherals, or for converting the peripheral-transmitted data into an ATM cell structure to send to the base station 30.
The customer premises equipment 40 is composed of an outdoor unit(CPE ODU) 12, an antenna 13, a network interface unit(NIU) 14, a telephone 15, a computer 16.
In FIG. 1, an ATM(asynchronous transfer mode) exchange 1 analyzes ATM cell-based data used in LMDS system and exchanges the data. The head ends 2 communicate with the units in the central office 20, send data to the customer premises equipment 40, and handle the data sent down from the customer premises equipment 40 so as to send to the units in the central office 20. The hub outdoor unit(HUB ODU) 3, with the antenna 4 thereof, converts the signals from the head ends 2 into upstream format so as to radiate it in RF signal, or converts the signal from the customer premises equipment 40 into downstream format so as to provide it to the head ends 2. The internet gateway 5 is used for providing the customer premises equipment 40 with an ATM-LAN service. An interworking function(IWF) 6 matches, when data is exchanged between the ATM exchange 1 and a private branch exchange(PBX) 9, the ATM exchange 1 and the PBX 9 so that they can operate in linkage. To perform this, the IWF 6 is equipped in hardware and software modules. A network management system(NMS) 8 plays a role in managing the network status between the ATM exchange 110 and the hub outdoor unit 3. It also manages the status of the wireless channel between it and the customer premises equipment unit 40. The PBX 9 plays a role in managing the billing information to the customer premises equipment unit 400, when using a WLL(wireless local loop) as a private network service. In addition, it operates in linkage with PSTN in order to perform a data communication. An internet service provider ISP 10 means an access network for an internet service.
FIG. 2 is a detailed organization of the wide band wireless multimedia communication system shown in FIG. 1. With reference to FIG. 2, a central office 100 is organized by an internet gateway 110 for providing a customer premises equipment 400 with an ATM-LAN service; an exchange 120 for analyzing the ATM cell-based data and exchanging them; a telephone switch 130 for interswitching the telephones connected to a public switched telephone network(PSTN); a digital access and cross-connected system(DACS) 140 for multiplexing and demultiplexing many dedicated lines; a network interface 150 for routing, multiplexing, and demultiplexing the data stream transmitted from the exchange 120, the telephone switch 130, and the DACS 140; an Ethernet bus 160 connected with the network interface 150; a subscriber management system(SMS) 170 for managing the operational status of and the information on the at least one customer premises equipment 400; a network management system(NMS) 180 for managing the network operational status between the head ends 200 and the base station 300, and for managing the status of the wireless channel between it and the customer premises equipment unit 400; and a network management control 190 for managing the at least one NMSes 180.
FIG. 3 shows an interconnection between the exchange 120, the network interface 150, and the head ends 200 shown in FIG. 1. FIG. 3 shows that a channel card is supervised by a base station 300 which is belonged to the head ends 200, in a base station of a communication company using LMDS system, e.g., CATV company. In FIG. 3, the exchange 120 of the central office 100 and the network interface 150 of the base station 300 are connected via STM-1 grade SDH transmitter. Herein, the network interface 150 plays a role of an ATM exchange, and is installed in the operation room of the base station 300, with the head ends 200. In addition, microwave converters(MWCs) 340 are installed in an outdoor transmission tower.
Like the above, in such a conventional communication system using LMDS system, the ATM exchange, the head ends, the base station are estranged at a long distance. Therefore, when new channels must be extended, the work must be performed at every base stations and it is necessary to add an equipment to every base stations. Moreover, every base stations must have a room for equipment setup, and, in the case of use of a ring type connection between the network interface and the hub outdoor, an SDH add/drop multiplexer is necessary. In addition, a maintenance or troubleshooting is quite inconvenience.
It is an object of the present invention to provide a local multipoint distribution service(LMDS) system, in which the cost for installation and maintenance is lower comparing to a cable communication system, it takes a little time to install the system, and a variety multimedia communication services can be provided.
It is another object of the present invention to provide a local multipoint distribution service(LMDS) system which provides a super-high speed wide band multimedia service using a subscriber""s loop frequency band of a millimeter wave band, so that it can provide subscribers with a wireless Internet, a wireless local loop, line leasing service, etc., in linkage with an ATM-based cable network.
It is yet another object of the present invention to provide a wide band wireless multimedia communication system having a proper frequency arrangement structure that does not affect the same channels of the base station and the subscribers when the base station is divided into two frequencies per a cell or the different frequencies are used at every sectors of the respective base stations.
According to one feature of the present invention to achieve the object, an LMDS system according to the present invention comprises a data/signal handler for multiplexing and modulating packet data received from a network, and for demodulating and demultiplexing an optical signal received; and at least one base stations for down-converting the multiplexed and modulated packet data into a radio frequency(RF) signal, and for converting an RF signal received into an optical signal so as to send to the data/signal handler.
According to another feature of the present invention to achieve the another object, an LMDS system according to the present invention for a wide band wireless multimedia communication system is characterized in that cells of a base station is designed by setting to xe2x80x9c1xe2x80x9d a frequency reuse parameter(K) in which a neighboring cell can use frequency in a current cell.